Lithium ion secondary batteries have a positive electrode, a negative electrode, and a nonaqueous electrolyte solution interposed between both electrodes. Charging and discharging is carried out by having lithium ions within the electrolyte solution come and go between the electrodes. A lithium-containing transition metal oxide is primarily used as the active material which reversibly store and release lithium ions at the positive electrode. The technical literature relating to positive electrode materials includes Patent Literatures 1 and 2.